if you want roughly 55 gallons, then you need to divide it around 36" mark. leave you only 12" more of Horizontal space. and really you could give that to only 1 other guy. Because bettas need room to swim horizontally, not vertically. maybe 2 guys, but thats only 6" of horizontal movement which is a shame!

Exactly what a said a week ago on another thread hehe You may be able to divide it the other way (make your dividers a T) but then the boy in the back never sees much. It's not about how many gallons really, more so how much horizontal space to swim. A 2g tall isn't as good as a 2g wide.